In the semiconductor industry, disc-shaped semiconductor wafers form the basic medium for manufacturing electronic integrated circuits and devices. Typically, each wafer is subjected to a series of processing steps necessary to form tens of thousands of microelectronic devices. Thus, it becomes apparent that such wafers acquire considerable value as each processing step is performed. Since these wafers are fragile, and their features are delicate, the processing steps usually take place in a clean room environment to avoid particulate contamination of the wafers. The transport of the wafers in and out of such clean room, and between processing stations within the clean room, is typically achieved by using wafer carriers or cassettes capable of accommodating about 25 wafers, with each wafer held in a separate pocket in a substantial upright position.
In an effort to minimize damage and particulate contamination of the wafers and thereby achieve high manufacturing yields, operator handling of the wafers is being substantially avoided by resorting to automation. In an automated semiconductor wafer processing facility, it becomes essential to first identify each individual wafer of a cassette to verify that the correct wafers are in such cassette. Next, the identification of each wafer is required to insure that the appropriate processing steps associated with a particular wafer are indeed carried out on such wafer. Therefore, there exists a need for an apparatus capable of automatically handling and identifying without human intervention, any wafer within a cassette.